Apparatuses used for melt spinning of synthetic threads are known from German Patent Application 195 40 907 A1, for example.
To this end, a polymer melt is fed to a spin beam from a melt source, for example an extruder or a polymerization unit. Inside the spin beam the melt is fed to usually one, or, by use of a distributor, multiple, metering pumps, which distribute the melt at a defined volumetric flow rate to spin cans in which the filaments are formed. The elements of the spin beam, that is, the distributor, metering pumps, piping, and spin cans, are all heated together and are enclosed by insulation.
Occasionally the physical characteristics of the polymers used for the melt spinning are altered under the influence of temperature and time. Polyamide 6.6, for example, tends to undergo post-polycondensation, resulting in an unmeltable hardening of the material and thus to deposits, or, in extreme cases, to plugging, in the lines. For this reason, in the design of spin beam special attention is given to a uniform, short residence time of the melt in the spin beam, and to a very uniform temperature. The residence time of the melt can be made uniform by mechanically optimizing the flow in the lines. Uniform temperature of the spin beam is achieved by heating, using a heat transfer medium contained as a liquid/gas mixture in the spin beam. Heat is transferred to the cold locations by condensation of the gaseous portion of the fluid on same, so that a very uniform temperature corresponding to the boiling point of the heat transfer medium is achieved within the spin beam. It is also known to use oil as heat transfer medium, or electrical heating.
Despite the above-described constructive measures, spinning of polyamide 6.6 is not regarded favorably by manufacturers of synthetic fibers. If post-polycondensed polymer forms, resulting in plugging of the lines, the spin beam must be completely disassembled and the plugged elements regenerated in an external furnace, i.e.; pyrolytically cleaned at temperatures of 450 to 550° C. This situation may occur in particular upon unit shutdowns, or when there is insufficient polymer throughput. However, even without the occurrence of an unexpected operating state it may be necessary to regenerate the spin beam at certain time intervals.
The cost of regeneration deters small, inexperienced synthetic fiber manufacturers from processing critical polymers such as polyamide 6.6.
The design of a spin beam must take into account ease of disassembly and the ability to dismantle into small units. Appropriate flanges on piping, using sealants, must be provided.